Protective apparatus for alternating-current-distribution systems.



v G; HARLOW & K; M. FAYE-HANSEN. PROTECTIVE APPARATUS FOR ALTERNATIIIGCURRENT DISTRIBUTION SYSTEMS. APPLICATION FILEIJ APR- IB, IQII.

1,151,783. Patented Aug. 31, 1915.

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G. HARLOW & K. M. FAYE-HANSEN. PROTECTIVE APPARATUS FOR ALIERNA-TINGCURRENT DISTRIBUTION SYSTEMS.

APPLICATION FILED APR- 18. I911.

Patented Aug. 31,1915.

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U N 1 TITED STATES PATENT OFFICE.

GEORGEjHAItLOW, 0F TIMPERLEY, AND KABI| MARTIN FAYE-HANSEN, 0FSTRETFORD,

ENGLAND, ASSIGNOBS TO WESTINGHOUSE ELECTRIC AND MANUFACTURING COM- PANY,A CORPORATION OF PENNSYLVANIA.

PROTECTIVE-APPARATUS FOB; ALTERNATING-CURRENT-DISTRIBUTION SYSTEMS.

Specification of Letters Patent.

Patented Aug. 31, 1915.

Application filed April 18, 1911. Serial No. 621,919. 7 I

v the King of Norway, residents, respectively,

of Timperley, in the county of Chester, England, and Stretford, in thecounty of Lancaster, England, have invented a new and useful Improvementin Protective Apparatus for Alternating Current Distribution Systems, ofwhich the following is a specification.

Our invention relates to protective apparatus for alternating currentdistribution systems of the kind in which the feeder co-nductors of thesystem are divided into a plurality of sections separated from oneanother bycircuit breakers. In distribution systems of this kind it isusual to provide devices for automatically openlng the circuit breakersat each end of a section in the event of any fault occurring in the saidsection and the present invention provides improved arrangements ofprotective apparatus of. this kind which are simpler and cheaper thanthose heretofore employed.

According to the present 'lnventlon, the primary winding of a seriestransformer is connected at each end of the feeder section to'beprotected, the secondary windings of I these transformers beingconnected together by means ofresistances and pilot wires in cuitbreakersbeing connected between these equipotential points so thatnormally no current traverses the said tripp ng co ls. Any accident tothe feeder section involving relative change in the-currents traversingthe series transformers at each end of the saidsection will evidentlydisturb the electrical equilibrium of the pilot circuit, so that thepoints between which the tripping coils of the circuit breakers areconnected are no longer at the same potential and currents arethereforesupplied to these tripping coils to open the circuit breakersand isolate the faulty section of the feeder.

The inventionis illustrated in the accompanying drawings of which--Figures 1 to 5 are diagrammatic 'views the transformers 4: and 5 are thesame.

showing our protective devices applied to different kindsof'distribution svstems. 7

Referring now to Fig. 1, which illustrates the invention as applied to asingle-phase distribution circuit, one section of a feeder conductor isindicated at 1 and includes the primary windings 2 and 3 of two seriestransformers tand 5 which are located at the respective ends of thesection. The terminals of the secondary windings 6 and 7 of thetransformers 4 and 5 are connected together by pilot wires 8 and 9, aresistance 10 of suitable value being connected in the pilot wire 8 atone end of the feeder section and a similar resistance llbeing connectedin the other pilot wire 9 at the opposite end of the feeder section, thesection being provided, according to. the'usual practice, with crcuit-breakers A and A at its respective ends. The tripping coil 12 ofthe circuitin the adjacent resistance 10 which is at the a samepotential, under normal'conditions of current flow in the section. Thetripping coil 13 of the circuit-breaker A at the other" end of thesection is similarly connected between intermediate points in thetransformer winding 7 and in the adjacent resistance 11, respectively.The operation of this form of the protective system of our invention isas follows: The-secondary windings 6 and 7 of the transformers land 5,together with the pilot wires 8 and 9 and their correspondingresistances 1O and'll, form a closed pilot circuit which is continuallytraversed by current so long as the direction and magnitude of the flowof current in the primary windings 2 and 3 of The electromotive forcegenerated-by each of the transformer secondary windings 6 and 7 is,

therefore, under normal conditions, equal to same potential ascorresponding points in the resistances 10 and 11, and the trippingcoils 12 and 13 of the circuit breakers, if connected across pairs ofequipotential points thus selected, will not be traversed by current,under normal conditions. In case the magnitude or direction of the flowof current in either of the primary windings 2 and 3 of the seriestransformers be altered relatively .tothe magnitude or direction ofcurrent flow in the other of the said.

transformers, however, the points in the secondary windings of thetransformers and their corresponding resistances across whichthe'tripping coils of the circuit-breakers are connected, will no longerbe at the same potential and the tripping coils of the circuitbreakerswill be traversed by currents which serve to effect the opening of thecircuitbreakers and the disconnectlon of the feeder section.

Referring now to Fig. 2, the invention is illustrated as applied to athree-phase circuit in which each of the conductors 14, 15 and 16 of thefeeder section is provided with series transformers 17, 18 and 19 at oneend of the section and similar series transformers 20, 21 and 22 at theother end of the section. The secondary windings 23 of the seriestransformers 17 18 and 19 are starconnected through resistances 24, asimilar connection being adopted for the secondary windings 25 of theseries transformers 20, 21 and 22. The outer ends of the star-connectedwindings 23 and 25 are connected together by means of pilot wires 26 sothat a closed pilot wire system comprising the secondary windings 23 and25 of the series transformers and the resistances 24 is formed. Thetripping coils 12 of the circuit-breakers A at one end of the sectionare,

in this case, connected together in star with their outer ends connectedto the adjacent ends or other intermediate points of the secondarywindings 23 of the series transformers, as shown, the tripping coils 13for the circuit-breakers A at the other end of the section beingsimilarly connected. The series transformers 17 18, 19, 20, 21 and 22must, in this instance, be of the kind having their magnetic coresprovided with air gaps in order to reduce the impedance offered by thesewindings to the passage of a current through the tripping coils when afault occurs in the section. The operation of this form of theprotective apparatus is as follows: So long as normal conditions of theflow ofcurrent in the section exist, the points in the transformerwindings 23 and 25 to which the outer ends of the star-connectedtripping coils 12 and 13 are connected will evidently be equipotentialpoints. If, however, a fault occurs in any of the conductors of thesection, so that the relative magnitude ordirection of flow of currentsin the two sets of series transformers 17, 18 and 1,9, and 20, 21 and 22is altered, the electrical balance of the pilot wire system will bedisturbed and local currents will traverse the tripping coils 12 and 13and cause the circuit-b'reakers to open and isolate the section. Theprotective apparatus of our invention may also be applied to athree-phase system, one phase conductor of which is grounded, or to atwo-phase three-wire system, or to a single-phase three-wire system withone of the conductors grounded, as illustrated in Fig. 3. According tothis arrangement, series transformers need only be provided in the twoconductors of the system which are not grounded. The secondary windings23 and 25 of these transformers are cross-connected in parallel with oneanother to the pilot wires, 8 and 9 which severally contain suitableresistances 10 and 11, the connections being similar to those alreadydescribed with reference to Fig. 1. In this case also, equipotentialpoints in the transformer windings 23 exist and are connected togetherby means of a conductor 27. The conductor 27 is also evidently at thesame potential as some point in the resistance constituted by theresistance 10 and the pilot conductor 8, under normal conditions ofcurrent flow in the feeder section. The tripping coil 12 of thecircuit-breaker at the corresponding end of the section is thereforeconnected between this point and the conductor 27. The connections atthe other end of the feeder section are precisely similar and, as willbe readily understood from the description already given, the trippingcoils 12 and 13 will only be traversed by current in the event of afault occurring in the section.

Referring now to Fig. 4, another protective system embodying theinvention as applied to a three-phase distribution circuit isillustrated in which the secondary windings 23 of two of the seriestransformers at one end of the section are connected in parallel withone another to the corresponding windings 25' of the transformer at theother end of the section by means of two pilot conductors 28 and 29, one(29) of which contains four resistances 30, 31, 32 and 33,.theresistances 30 and 31 being located at one end of the section and theresistances 32 and 33 at the opposite end/ A point 34, intermediate theresistances 30 and 31, is connected, through a third resistance 35 andthe secondary winding36 of the remaining series transformer, to thesecondary winding 37 of the corresponding series transformer at theopposite endof the section. Two tripping coils 38'and 39 are providedfor the circuit-breakers at each end of the section, the coil 38 beingconnected between intermediate points in the windings 23 and a point inthe pilot conductor 29 intermediate the resistances 31 and 32 and theother tripping. coil 39 being connected across an intermediate point inthe secondary winding 36 and the point intermediate the resistances 31and 32, above referred to. With 39 from the secondary windings of theseries transformers, in the event of a fault occurring in the feedersection, has only to pass through the resistances 30and 31or. 31 andbreakers of a distribution system of the kind.

35'and the tripping coil itself, and the impedance of the transformerwindings need not therefore be. considered.

Referring now to Fig. 5, another method of connecting the variouselements of the protective apparatus, as applied toa threephasedistributiomis illustrated, in which the secondary windings 23 'oftwo ofthe series transformers at each end of the section are directlyconnected in parallel with each other and cross connected inparallelwith the secondary winding 36 of the third series transformer;the two closed circuits thus formed at each end of the feeder sectionbeing connected together, as shown, by means of two pilot wires 28 and29, which respectively contain resistances 10 and 11, one adjacent toeach end of the feeder section. The single tripping coil 12 of thecircuit-breaker at each end of the section is connected be tween pointsintermediate the ends of the secondary windings 23 and 36 0f the threeseries transformers at one end of the section and a point in the pilotconductor 28 beyond the resistance 10, as shown, the connections at theopposite end of the section being precisely similar. In order to insurethe excitation -of the tripping coils 12 and 13 when a short circuitoccurs between the phase conductors 14 and 15, the'transformersconnected in these conductors must be so designed as. to'have differenttransformation ratios. i

. The resistances referred to above are preferably.approximately equalto or smaller than the resistance of the pilot wires employed, and aswill be readily understood, any pairs of equipotential points may beselected which will give the desired efiect. Furthermore, the inventionmay be utilized for effecting the opening of the circuit described, whenan overload occurs, by so arranging the connections of the trippingcoils of the circuit-breakers that the 'said coils are not connected topoints of exactly equal potential but are traversed bycurrentsvarying'with the load on the feeder section. It will beunderstood that, although, in-

the above examples, separate series transformers for each phaseconductor have been referred to, a single transformer at each end of thefeeder section may be employed, if-

desired, such'transformer having a number abnormal conditions.

of primary windings corresponding to the When a system hasa-groundedneutral and one of the other conductors becomes grounded, there 1s acondition existing s1m1- -larto that condition when one conductorbecomes short circuited on another, in which case, the transformernearest the source of energy will have a relatively larger currentflowing in it than before the ground or short circuit occurred, whilethetransformer farther away from the source of energy will have lesscurrent in it. This increased current will cause an increase in thecurrent flowing 1n the secondary winding, while there is a decrease inthe current in the secondary winding .of the other transformer. Thus,since the transformers are no longer of the same potential, the pointsof equipo-.

tential are not the same as before and there will be a potential acrossthe points which were normally at the same potential causin gthecircuits tovbe interrupted. A two phase circuitycomprises two singlephase circuits and, consequently, two protective circuits similar tothose shownin Fig. 1 may be used to isolate sections of the same underWhenany wire of a three-phase system becomes grounded, that allows thecurrent to drop in the transformer which is located at the greaterdistance from the source of energy. This change in current isaccompanied by a proportional potential change, while the currentin thetransformer-nearest the source of energy either remains constant orrises in value, thus upsetting the system of equal potential, ashereinbefore described. When there is a transient surge set up in aconductor, due either to lightning dischar e or dielectric influences ofa passing clou one transformer will receive more current than 'the otherand, consequently, will alter, the equlpotential system until there.will be sufficient voltage across a trip coil to isolate a thereinhaving tripping coils connected be-' tween oints in said secondawindings and pilotwire system which are at the same potential undernormal conditions of current flow in the section.

3. Protective apparatus for an alternating current distribution systemcomprising series transformers and resistances at the ends of eachsection to be rotected, a vpilot wire connecting the trans ormersecondary windings and the resistances for each section in series in aclosed circuit, and circuit breakers the tripping coils of which areconnected between intermediate points in the 1 adjacent transformersecondary windings and points in the pilot circuit that are at the samepotential under normal conditions of current flow in the section.

4. Protective apparatus for. an alternating current distribution systemcomprising series transformers and resistances at the ends of eachsection to be protected, the secondary windings of the transformers atthe same end of each section being connected in parallel relation, pilotwires connecting the transformer secondary windings and resistances atopposite ends of each section in series in a closed circuit, and circuitbreak ers the tripping coils of which are connected between intermediatepoints in the adjacent transformersecondary windings and points in thepilot circuit that are at the same potential under normal conditions ofcurrent flow in the section.

5. Protective a paratus for an alternating current distr1 ution systemcomprising series transformers and resistances at the ends of thesections to be protected, certain of the secondary windings of adjacenttransformers being connected in arallel relation and in series withcertain ot ers of said secondar windings, ilot wires connecting thetrans ormer secon ary windings at opposite ends of the protectedsections in series in a closed circuit, the resistances being includedin the said connections, and circuit breakers the tripping coils ofwhich are connected between intermediate points in the adjacenttransformer secondary windings and points in the pilot circuit that areat the same potential under normal conditions of current flow in thesection.

In testimony whereof, we have hereunto subscribed our names this 23rdday of March, 1911.

GEORGE HARLOW. KARL MARTIN FAYE-HANSEN. -Witnesses:

J AS. STEWART Bnoanroo'r, PERCY WM. Hour.

